During operation of a combined cycle plant a gas turbine engine produces all the heat necessary to generate all the steam that is required to run the plant. This includes steam required to operate the steam turbine as well as the steam required to supply the plant's peripheral processes When the gas turbine engine is not operating some of the peripheral plant processes still require steam Conventionally this steam has been generated by an auxiliary steam generation system that is a miniature, self-contained boiler system that may include a gas or oil fired burner, a water feed pump, chemical treatment equipment etc. This auxiliary steam may be used for any or all of the steam turbine gland seals, low pressure sparging of condenser hotwell, pegging of the deaerator tank (DA tank), or other purposes. When the gas turbine engine is operating and providing all of the steam necessary for operation of the combined cycle plant the auxiliary steam generation system may be shut down. An auxiliary steam generation system may cost upwards of two million dollars yet it may sit idle for most of its lifetime
During operation of the gas turbine engine air is compressed in the gas turbine engine's compressor in a process that generates a significant amount of heat. One configuration of a combined cycle plant makes use of this heat by routing the heated air through a kettle boiler, also known as a rotor air cooler, as described in U.S. Pat. No. 6,145,295 to Donovan et al and incorporated by reference herein in its entirety. Kettle boilers conventionally have two primary functions. The first is to provide a supply of cool air that is used to cool components in the gas turbine engine while the engine is in operation. The second is to provide an additional supply of steam to the Heat Recovery Steam Generator (HRSG), which is part of the combined cycle plant configured to receive exhaust from the gas turbine engine and use heat in the exhaust to generate steam for the steam turbine.
The kettle boiler itself has both an air side and a water side. Heated air from the compressor is delivered to the air side and cooled by heat exchange with water on the water side of the kettle boiler The kettle boiler cooled air is then used to cool hot parts in the gas turbine engine. The water heated in the kettle boiler may come from the low pressure (LP) and/or intermediate pressure (IP) sections of the HRSG The additional heat added to the water in the kettle boiler increases the volume of steam generated and thus increases the overall efficiency of the plant